UF Experts Say Fear Unwarranted But Treat Malathion With Respect

June 27, 1997

GAINESVILLE—Is the pesticide malathion dangerous or safe?

The way malathion is being used in Hillsborough, Polk and Manatee counties to fight an outbreak of the Mediterranean fruit fly is safe, say scientists at the University of Florida’s Institute of Food and Agricultural Sciences. On the other hand, guzzling a juice glass of it is not so safe.

The key with malathion, like any pesticide, is to use common sense and avoid unnecessary exposure.

And the cost of not using malathion is high, said Professor Joseph Knapp, of UF’s Citrus Research and Education Center in Lake Alfred.

The crops malathion is being used to protect contribute $10 billion to the state’s economy, Knapp said. If that revenue is lost, every man, woman and child would have to pay an additional $700 in taxes to maintain the same quality of life.

Knapp said the medfly is the most widespread fruit fly in the world and one of the most damaging. More than 250 varieties of fruits, vegetables and plants can serve as hosts to the pest. Once medfly larvae burrow into fruits and vegetables, the produce rot, ruining entire crops. In the outbreak area, citrus is the most valuable crop affected but the medfly also will attack other important crops including tomatoes, strawberries, figs, mangos, persimmons, guavas, pears, peaches and apples.

The medfly does not discriminate between commercial and backyard host plants. While the current situation is difficult, scientists said aggressive and prompt action now will use less pesticide over a smaller land area at a lower cost than if no action is taken. Home gardeners, too, will be using more pesticides and harvesting less if the fly is not quickly eradicated.

Malathion is the most effective and safest chemical to use in medfly eradication, scientists agree.

“Malathion has been used for medfly eradication before and we know it can be done with no long-term effect,” said entomology department Chairman John Capinera, who has been appointed to the Florida Medfly Scientific Advisory Panel.

Doing nothing or using less effective eradication measures would be even more costly and more toxic in the long run, Capinera said.

“If we act now, this will not become a permanent problem,” Capinera said. “But if medfly gets established, we’ll be spraying insecticide a lot more frequently and we’ll be exposed to more insecticide and more toxic insecticide over the long term.”

Malathion is a common pesticide that breaks down in the environment with exposure to sunlight and water. That means its residue is not building up in soil, water, plants or animals.

Another plus for malathion is that it is an older pesticide. Around since 1950, malathion has been thoroughly studied for any side effects. While impurities in malathion can increase its toxicity, the malathion being used in Hillsborough, Polk and Manatee counties is a high-quality formula safely used in Florida and California for years.

The same Central Florida residents concerned about malathion spraying probably have some in their homes to fight household and garden pests. Malathion can be found in many general purpose sprays used to control mosquitoes, flies, household insects, animal parasites, and head and body lice. Diazinon, another common chemical found in the sheds of many weekend gardeners, is four times as toxic.

And it is malathion being sprayed from the mosquito trucks that many residents welcome to their neighborhoods in summer. These trucks release 3 ounces of malathion per acre while the medfly planes are releasing 2.4 ounces per acre.

“People think this is just an industry problem and it doesn’t affect them but if you drive around that area you’ll see a lot of fruit trees in back yards and those are going to have medflies, too,” Capinera said. “And then, if medfly is established, fruits and vegetables containing maggots will make it to market. Ask the people in Hawaii, where it’s a permanent problem, about that.”

Capinera and UF pesticide specialist Norm Nesheim said fear is unwarranted but it makes sense to treat malathion with respect.

Nesheim says persons in areas subject to aerial applications of malathion can take safety precautions, including staying indoors during aerial treatment and washing skin or clothing that becomes exposed to the bait. If the spray gets into the eye, it may cause some stinging, which can be relieved by rinsing eyes with water. No permanent damage will result.

Nesheim said studies in California show malathion sprays of the type being used in Florida do not result in aerosols. The malathion is being released in a syrupy mix designed to attract the medflies. Air sampling in California following applications of this type found malathion concentrations in air to be 15,000 times less than the occupational standards for malathion air concentration, Nesheim said.

Knapp said one of the reasons malathion is not very toxic to humans is that humans have a blood enzyme that rapidly destroys malathion. Studies by several agencies have cleared malathion of side-effects such as birth defects, cancer and immune system suppression.

While some residents are concerned about paint damage to cars that come into contact with the bait mixture, it is the acidity of the mixture that is harmful to paint, not the malathion in the mixture.

Bees and some species of fish are sensitive to malathion and need to be protected during spraying. Malathion is soluble in water so removing it from cars, vegetables and hands is easily accomplished by simple rinsing.

The outbreak in Hillsborough, Polk and Manatee counties is the 16th medfly outbreak in Florida since 1929.

Capinera said research is in progress on using less toxic methods to control medflies.

“There is hope on the horizon for safer materials,” Capinera said. “But nobody likes to pay for research like this until there’s a problem and we have to turn to 1950s methods.”